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circuit diagram for electronic trip gear

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rogsilk

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DSCF1419.JPG
please can anyone explain how this circuit works.
its for a diesel fuel pump testing machine,and untill it works again my machine is redundant.
 
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Mickster

Well-Known Member
Most Helpful Member
It would probably help more if you could describe, in as much detail as possible, how it is not working.
 

rogsilk

New Member
Mickster
The solinoid shorted out and killed tr302 (2n3055 ) i have replaced this, but allthough there's power the solinoid wont energise. I suspected the rectifier,but this seemd ok.
Ive checked the external start circuit and again this is ok
From here on in i'm lost,so any help would be most welcome
Sorry about the wiring diagram, its not that good, trouble is its as old as the machine 30 years.
rogsilk
 
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Mickster

Well-Known Member
Most Helpful Member
From here on in i'm lost,so any help would be most welcome
Me too, I'll admit that I'm not experienced enough to help you trouble-shoot this problem but the other members who are, will most certainly expect you to provide some voltage readings at certain points, whether the machine is used in single or multi-solenoid mode, whether LP301 is illuminating, etc, etc.

It's quite possible that the shorted solenoid, taking out TR302, also took something else out. Replacing only TR302 has probably resulted in the new transistor failing as soon as the machine was operated again.

If you have taken any readings, please post them, as this will help the real engineers to diagnose the problem.

HTH.
 

user_88

Member
... need to know base voltage of TR 301.
.... also what is base voltage of TR302?
.... need to know if 'multi' or not.... Is there a TR303?
It is not unusual to see 'chain-event' type of part failures....

What is part designated LP301?
 

Mickster

Well-Known Member
Most Helpful Member
What is part designated LP301?
On automotive schematics, that symbol indicates some form of indicator lamp. (not turn-signal indicator :D)

EDIT: How are the links A-B & A-C controlled, in "Mode Selection"? Some form of selector switch?
 
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rogsilk

New Member
voltage at base of tr301 is ( 0.8v)
voltage at base of tr302 is (255mv)
There is no tr303.
the link A and C are for solinoid energised except when counting.
lp301 seems to be a neon light.
In the wiring diagram there is a direct conection between R301 and link A C, this does not show very clearly on diagram.
 
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user_88

Member
If TR302 only has 0.255 v base to emitter bias, it won't turn on.
TR301 should supply bias current to the base of TR302, but it doesn't look like a sufficient amount is getting through.
The bias voltage of TR301 seems to be enough, about 0.65 v.
TR301 might be defective.

Can you check TR301, or replace it with a known good part?

Where is the solenoid that failed, the one that you are trying to turn on?
Is it the part labeled 24 ... single solenoid load?
 
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user_88

Member
correction

Checking the base bias for TR301 .... it is 0.545 v.... not 0.65 v as stated in previous post.
This is a little low, and TR301 may not be fully turned on.
If TR301 checks out to be good, then test diode D301 ... the reverse oriented diode ... and see if it is good ......
Next to test would be C301, to see if it is intact .... not shorted out.
.... best way to test these components is to remove them from the circuit.
 

rogsilk

New Member
many thanks 88, i have re checked voltages and voltage's are same. so i am going to remove and replace.
new solinoid, old one in bin.
many thanks for your help.
will be in touch.its getting to late to do any more tonight 11pm here
rogsilk
 

rogsilk

New Member
88
have done what you suggested, both 301 and 302 and diode check out ok
all readings are still the same.
sorry it's taken so long but work has to come first
 

user_88

Member
If TR301 and TR302 are ok, then it appears that something connected to the base of TR301 is not working right.

Try de-soldering D301 at one end, and checking the diode .... You should use the diode test function on your DMM .... since the resistor continuity checker will not have sufficient voltage to turn it on. Also, check the reverse bias of D301 with the diode tester.

If D301 is good, then de-solder one end of C301, and check with a capacitor checker.
If you don't have a capacitor checker, you might be able to charge it up with a few volts DC, and see if it holds the charge for a few seconds ..... not absolutely sure what to expect though. Maybe just replace if with a known good 1µF capacitor.
 

rogsilk

New Member
solinoid activats if a high pulse is injected to pin 8 of ic6 sn7406.
but from diagram this pin is allways low,as this comes from pin 12 of sn 7473 which is high. even when pin 14 (J) goes low im still getting a high from pin 12.
i have changed the 7473 chip thinking it was faulty but no change.
providing there is a high to the base of 301 every thing works ok.
any ideas?
i am now getting in over my head.
rog
 
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user_88

Member
Thanks for the update ...
This brings us to the diagram area in the vicinity of TR1 and photo transistor D401.
The J-K flip-flop, IC4 may not be switching due to a missing clock pulse, which comes from TR1 and IC2, which is a 4 input nand gate.

What does D401 do? Is there a moving part or object which would be able to interrupt an optical light beam? I think it is fairly common for the LED light sources to burn out after a long term, or maybe the LED lens is has become opaque due to some sort of residue build up.
 
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rogsilk

New Member
there is a brass disc seperating the optics the disc has a small slot that allows light to pass through each revolution. the disc is driven by the shaft of the machine.
I have in my junk, another two of the optics so i will now change this.
be in touch
rog
 

user_88

Member
D401

88
can you tell me if there is any way i can test the optic device before i install it?
D401 is a typical photo diode emitter-receiver pair.
It will have one LED diode, and one photo transistor.
There should be one terminal on the part that will be a common ground.
There should be another terminal that will be the LED power terminal, which requires +5 V DC. If your DMM has an LED test function, you should be able to use it, connecting it between the LED power terminal, and the D401 ground terminal.

Testing an LED just using a resistor or continuity tester is not always effective. You really need to use an LED test function, if you have one that is available.

The photo transistor is essentially an NPN transistor, with the emitter connected to the part's ground terminal. The collector of the photo NPN should have its own terminal someplace on D401. The base of the photo transistor will be optically activated by the light beam of the LED emitter, and also switched by the rotation of the brass disk on the mechanical shaft.

I'm not completely sure, but if you have an hfe transistor test function on your DMM, you might be able to connect the ground terminal of the D401 part to the emitter connection of the hfe test port, and the collector terminal of the D401 to the collector of the hfe port. The base of the D401 would be controlled by rotating the shaft on the part.
For the transistor test to work, the LED would also have to be powered by +5 V DC, at its respective terminal.

If it looks like too much effort to test the photo transistor, then just test the LED, using the LED tester of the DMM, since the LED is a little more likely to fail than the photo-transistor.
 

rogsilk

New Member
I made up a circuit to test optics and as you stated it was the diode that failed,i have replaced it with good one,and now getting a pulse on pin 1 on ic4 (7473).
Readings on other pins are pin 13 high pin 12 low pin 14 goes low when start switch is pressed pin 2 (clear) is high, i dont know if it is supposed to be low or high.
It seems untill pin 8 on ic6 (7406) goes high the solinoid wont work.
The solinoid is supposed energise when machine is turned on and de energise to start count.
Any sugestions?
rog
I copied the circuit for optics from the wiring diagram.
 
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user_88

Member
The next step to try would be to replace the 7406.
By doing this the low signal on pin 12 of the 7473 should be inverted .... coming out as a high on pin 8, which should turn on the solenoid.

For the solenoid to de-energize, to start the count, the clear2 pin would return to a low state.

So, try replacing the 7406 inverter, and see if it works.
If the solenoid energizes, but fails to de-energize, then there might be something wrong with the clear2 sequence.
 
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